Shade Tolerance and the Relationship between Herbivory and Light Availability

Premise of research. Herbivore damage is generally higher in the sun than in the shade. The influence of shade tolerance on herbivory has been mainly related to the fact that light-demanding plant species show lower defense investments—and hence higher herbivory—than shade-tolerant species. The pattern of increased herbivory with increasing light availability may take different forms, depending on the drivers of herbivore damage across the light gradient: (1) herbivory pressure alone, (2) herbivory pressure together with plant resistance associated with shade tolerance, or (3) the two drivers seen in scenario 2 added to a differential effect of light availability on plant resistance depending on shade tolerance. Elucidating the specific patterns behind the general pattern of increased herbivory with increasing light availability may contribute to understanding and aid prediction of herbivory patterns in forest communities under natural or anthropogenic disturbance. Methodology. In a field study with 15 tree species distributed across the light gradient in a temperate rainforest (1.6%–26.2% canopy openness), we evaluated the relationship between canopy openness and seedling herbivory, with 755 seedlings surveyed for herbivore damage. Specifically, we evaluated the consistency between the observed herbivory–canopy openness relationship and the three scenarios described above. Pivotal results. We found steeper slopes for the herbivory–canopy openness relationship in tree species with lower shade tolerance; that is, we verified scenario 3. Conclusions. Shade tolerance determined the slope of the herbivory–canopy openness relationship across the light gradient. This finding expands our understanding of the recognized influence of shade tolerance on the interplay between herbivory and the light environment.